Activity block



FIG. 1 is a perspective view of an activity block, showing my new design, the broken line showing of the insertable toy is for illustrative purposes only, and forms no part of the claimed design;

FIG. 2 is a plan view thereof;

FIG. 3 is a front view thereof;

FIG. 4 is a right side view thereof;

FIG. 5 is a left side view thereof;

FIG. 6 is a bottom view thereof; and,

FIG. 7 is a rear view thereof. 

The ornamental design for an activity block, as shown. 